The concept of a "fast" suit relies on some assumptions. First, it assumes that your swimsuit can not only cover you without adding to your drag, but that it can reduce your drag. Second, it assumes that the drag-reducing features on your suit will help you swim more quickly, without making you use more energy or oxygen.

The international governing body for swimming, FINA (or Federation Internationale de Natation), approved the first full-body suits that claimed to reduce drag in time for the 2000 Olympic trials [source: Longman]. Swimmers sported various body and leg suits at the 2000 and 2004 Olympics, culminating with Speedo's LZR Racer in 2008. Speedo claims that this is the fastest suit on the market.

The suit is a sheet of woven spandex, with "very, very smooth" gray panels sealed onto the torso, legs and rear, says Jason Rance, former head of Speedo's research and design unit, and one of the LZR Racer's designers.

The LZR Racer is smoother than hairy or shaven skin, one reason why Speedo says it's advantageous to squeeze into the suit rather than to swim in briefs. The smoothness comes from the materials; Speedo's woven spandex has a "flatter structure" than knitted material, and the panels, which were optimized in NASA wind tunnels, are like "Glad wrap," says Rance. To make the suit smoother, Speedo constructed it from three pieces of fabric to minimize seams and welded, rather than sewed, the pieces together. Welding cut viscous drag by 6 percent as compared to sewing, says Rance.

It's not only the suit material that Speedo tried to smooth, but the swimmer. Swimmers aren't built like torpedoes, but like bumpy human beings. The curves of their frames and muscles add to pressure drag, which is even worse than friction on a rough suit. And in churned-up water, even the buffest swimmer's skin and muscles shimmy, adding to pressure drag.

­Speedo tried to "smooth a swimmer's lumps and bumps" by making the suit compressive, says Rance. The tightness takes getting used to. Speedo tested swimmers' oxygen use in the suit partly to make sure they didn't "build up so much compression that the swimmer can't breathe effectively," says Rance. The company found that swimmers do breathe normally in the suit.